USGS Geology in the Parks
Sunset Crater Volcano
The eruptions that produced Sunset Crater and several nearby flows and smaller cones began between the 1064-1065 AD growing seasons (Fall 64 to Spring 65?). Eruptions may have continued on and off for about 150 years.
0.07 mi3 (0.3 km3) of magma erupted from the Sunset Crater vent system.
About 75% of the magma erupted at Sunset Crater erupted explosively as scoria. About half of the scoria fell very near its source and built Sunset Crater cinder cone, about half blanketed the region with ash and other small volcanic particles.
About 25% of the magma was erupted as lava flows. 75% of the lava now forms the Bonito Lava Flow.
All of the vents in the Monument produced similar magma compositions.
Eruptions reached surface through a 6.2 mile long (10 km) dike that tapped a basalt source in the upper mantle.
Initial eruptions probably formed a curtain of fire.
1064-1065 AD continuing to 1090 or later:
Black scoria tephra blankets region
Initial construction of Sunset Crater cinder cone with black scoria.
Kana-a flow begins.
East flank of Sunset Crater collapses onto Kana-a flow.
Probable time of 512 flow and Gyp Crater eruptions.
Construction of Sunset Crater cinder cone renewed or continued. Deposition of agglutinate layers.
Tephra deposited on top of Kana-a flow and vent 512 flow.
Bonito lava flow begins.
Scoria deposited on flow units coincident with Bonito flow.
West flank of Sunset Crater cinder cone rafts away agglutinate layers.
Construction of Sunset Crater cinder cone renewed or continued. Deposition
of unconsolidated black scoria layers.
Tephra deposited on top of Kana-a and Bonito flows.
Deposition of red scoria on Sunset Crater cinder cone summit, cementation of crater rim scoria by vapor-phase minerals.
Bonito and Kana-a flows extruded.
Eruption of black lapilli and bombs result in minor collapse of the east rim of the crater and formation of the small crater on the east side of the summit.
No, or minor deposition of tephra beyond the cone margin.
Eruption of rows of small red scoria cones on top of the black scoria tephra blanket east-southeast of Sunset Crater was after or coincident the above.